1. Field of the Invention
The present invention relates to non-halogen, flame-retardant electric wires, and particularly to flexible, non-halogen electric wires that are superior in flexibility.
2. Description of Related Art
Non-halogen, flame-retardant electric wires and cables (collectively referred to below as non-halogen electric wires) are widely used as polyvinyl chloride (PVC) alternatives. The non-halogen, flame-retardant material used as an insulator of the non-halogen electric wire is a resin composition prepared by adding a large amount of metallic hydroxide, as a flame retardant, to polyolefin polymer such as polyethylene, ethylene vinyl acetate copolymer (EVA) or ethylene ethyl acrylate copolymer (EEA), or to olefin rubber such as ethylene propylene rubber (EPDM).
When the non-halogen electric wire is required to be heat-resistant, a bridged resin composition is used as the non-halogen, flame-retardant material, which is insulative. A non-halogen resin composition with excellent flame-retardant properties is proposed in which the resin has high mechanical strength and no residual strain after forming, as described in JP-A-2000-327858.
Conventional non-halogen electric wires have less flexibility because the insulator is prepared by adding a large amount of metallic hydroxide to the resin composition used as the non-halogen, flame-retardant material. Accordingly, it is difficult to obtain both flame retardancy and flexibility from the conventional non-halogen electric wires as in PVC electric wires and cables.
Although olefin rubber such as EPDM is flexible, it generates much heat when it is burned because the molecular structure of the polymer does not include oxygen. Accordingly, it is difficult to obtain sufficient flame retardancy.
On the other hand, a possible way to increase the flexibility of the electric wire is to increase the flexibility of a metal conductor (simply referred to below as the conductor), which is fabricated by twisting a plurality of strands. However, if the diameter of each strand is reduced to increase the flexibility of the conductor, the conductor or strands become likely to be broken when the electric wire is manufactured or processed.
Accordingly, non-halogen electric wires superior in flexibility are extremely difficult to provide due to the above problems.